1. Field of the Invention
This invention relates to roofing ply roll or sheet products made by coating fiber glass mats with molten asphalt, and, more particularly to a process for making such products which are thin and low in weight, flexible, and of high tensile strengths.
2. Description of the Prior Art
Roofing ply sheet products are made by impregnating fiber glass mat rolls with an excess of molten asphalt, i.e. at an asphalt temperature of about 500.degree. F. Typically, such molten asphalt is applied in a coating apparatus which includes suitable coating rolls and mechanical scrapers. The excess of asphalt which penetrates the glass mat, however, is being removed before the sheet is used commercially. Usually this is accomplished by squeezing the asphalt-soaked mat in the nip of the coating rolls and then scraping off asphalt remaining on the surface of the mat. Unfortunately, these squeezing and scraping steps result in considerable mechanical damage to the glass mat itself, which reduces its tensile strength to below a minimum value necessary and required for commercial use. Several methods have been used in the past to compensate for the observed loss of tensile strength of the sheet during the squeezing and scraping steps. Since the tensile strength of the roofing ply sheet is directly related to the amount of asphalt retained in the mat, an added amount of asphalt can be kept in the mat to provide increased tensile strength. Another technique is to use a thicker glass mat which would have a higher tensile strength but with reduced flexibility. Both methods, however, add to the weight of the product, which is undesirable, and increase its costs.
Accordingly, it is an object of the present invention to provide a process for making improved roofing ply roll and sheet products by a process in which a predetermined amount of asphalt can be impregnated into a glass fiber mat so that the conventional squeezing and scraping steps previously necessary to remove excess applied asphalt are no longer required.
Still another object of the invention is to provide a roofing ply sheet comprising fiber glass mat coated with asphalt which sheet is thin and light in weight, flexible, and has a high tensile strength.
A feature of the present invention in this art is the provision of a step of controlled moisturization of a glass mat prior to asphalt treatment, which provides an intermediate product whose receptivity to asphalt impregnation is predetermined by the amount of water retained therein.